This planetary transmission, mostly built as a single- or multiple-stage planetary transmission, is basically implemented in machine tools, as well as in lathes, milling machines and machining centers. The selectable planetary transmission increases the service scope of the main spindle motors, as well as the flexibility of the machine tool for processing the different work materials through increasing high torques or high speeds. For example, two transmission stages may be built in, while on one hand the drive shaft which is connected to a sun gear with an internal gear and on the other the internal gear can be coupled to the housing. A planetary carrier is connected to the output shaft.
In DE A 199 17 673 of the applicant, there is such a two-stage planetary transmission, with a drive shaft and an output shaft which are mounted in the housing over roller bearings. The drive shaft is connected to a sun gear which engages with the planetary gears which are mounted over bearings on planetary bolts in a planetary carrier, which is connected over a positive fit connection with the output shaft. The planetary gears mesh with an internal gear, which is mounted over the roller bearings in the housing or in the rotating planetary carrier and positively fit with a hub connection. The hub is connected in a slip free manner, over an external gearing, with the first part of the sliding collar.
A roller bearing is located over the sliding collar. The external part is axially displaceable in the housing, running over bearing bolts, whereby the axial displacement of the external part is carried over the roller bearings.
The sliding collar can be placed in three operating positions and one neutral position. In the first operating position, the internal gear is coupled with the housing by a turret gearing. In the second operating position, the internal gear is coupled with the sun gear by a turret with a synchronizing gear and a positive locking connection. The turret is thereby connected in a slip free manner with the drive shaft.
The sliding collar displacement takes place through a switching mechanism, whose actuator is an electromagnet or a motorized switching unit and whose armature is connected with the sliding collar by means of a pinion.
In modern machine tools, the basic requirements of rotational speed, vibration value and accuracy are always increasing. The planetary transmission, which is a part of the machine tool transmission, is therefore a potential source of vibration that when the rotational speed increases can negatively influence the working surface.
The causes for vibration is based, among other things, on the unbalancing of the planetary transmission. The coupling parts such as the sliding collar require clearance so that they can move. The clearance in turn leads to an nonconcentric rotation, which generates unbalancing. For example, a sliding collar with the common weight of 1.6 kg can only move 0.1 mm from the center position, therefore the resulting unbalance is equal to 160 g-mm, which generates an extreme vibration. A planetary transmission operating under high rotational speed (i=1:1) demands a detailed processing of the work piece surface, which can only be achieved with low vibration machine tools.